1. Field of the Invention
The invention relates to fertilizer compositions comprising a sulfur-containing compound, and a reaction product of a potassium-containing compound and a humectant. Methods of using a solution of the fertilizer composition for supplying plant nutrients to a plant are also disclosed.
2. Description of the Related Art
New technology in the agricultural market is pushing crop yields higher and higher. The advancements in crop genetics, precision farming practices, and detailed field data are allowing commercial crop growers to push their fields to new limits. However, these advancements are not without limitations, because as yield rate increases, more and more nutrients are extracted from the soil, forcing growers to find new and improved methods to continuously provide and have available the correct levels of vital nutrients to the plants throughout the entire growth cycle. Unfortunately, there is limit to the amount of nutrients that can be applied to croplands by conventional methods without the fear of harming the crop, polluting waterways, or exorbitant spending.
Various elements, which are normally drawn from the soil, are known to be essential to plant nutrition. These elements include: nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), copper (Cu), cobalt (Co), zinc (Zn), boron (B), nickel (Ni), molybdenum (Mo), and chlorine (Cl). Of these elements, nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium are needed by plants in relatively large quantities and are therefore called macronutrients. The remaining members of the group (iron, manganese, copper, cobalt, zinc, boron, nickel, molybdenum, and chlorine) are known as micronutrients since they are required in very small amounts for plant growth.
Supplying a plant's major nutrient needs (nitrogen, phosphorus, potassium—N—P—K) is most effective and economical via soil application. However, foliar application has proven to be an excellent method of supplying plant requirements for secondary macronutrients (sulfur, calcium, magnesium) and micronutrients, while supplementing N—P—K needs for short and/or critical growth stage periods. Foliar application refers to the application of plant nutrients to above-ground plant parts. Foliar fertilization programs prolong the fertilizing application period, providing a continuous supply of nutrients when crop demand is at a maximum, and can be an economical way to boost yield.
In fertilization programs, sulfate metal salts (e.g., zinc sulfate, manganese sulfate, and copper sulfate) are an economical source affording both sulfur and micronutrients. These sulfate salts are readily soluble in aqueous solutions and can be applied either in a dry or liquid form. The simple chemical structure as well as the metal being non-chelated combines for quick and easy plant uptake of the metal cation and sulfate anion. However, aqueous solutions need to have a pH below approximately 3 to prevent the formation of metal oxide precipitates; also, dry material is challenging to apply foliarly.
Humectants have also been used to help retain water within the soil and plant tissue. These features make the incorporation of a humectant into a foliar fertilizer potentially beneficial to the needs of the plant.
Potassium deficiency is typically seen in the later stages of plant development as the available soluble potash near the root zone is depleted and translocated into the new foliage. Thus, getting potassium to crops during the high demand growth stages is essential to reaching the maximum yield potential. Potassium is usually applied as potassium chloride, potassium hydroxide, and/or potassium phosphate. However, these potassium compounds are ineffective when used in a foliar fertilizer program. Most potassium salts will cause chlorosis of the leaf tissue, thereby harming the plants development, reducing the yield potential, or causing death. When these potassium salts are combined with non-chelated metal sulfates and humectants, they become unstable and form insoluble precipitates. Using chelated metal salts, such as zinc ethylenediaminetetraacetate, does improve stability and solubility; however, many chelating agents have a molecular size too large to be effectively absorbed by leaf tissue. To the extent that chelating agents can be absorbed by leaf tissue, the delayed release and slow uptake of chelated metal into the plant cells is not desired in foliar applications, especially during high demand growth stages.
Due to the incompatibility of potassium salts and non-chelated metals, the current practice for applying potassium, sulfur, and micronutrients during the high demand vegetative and flowering stages requires: (i) multiple applications applying both sulfur and micronutrients and potassium salts separately, or (ii) using a single application of potassium salts and chelated metal salts where at best slow uptake of the chelated metal into the plant cells is expected.
Thus, there is a need for stable fertilizer compositions that include a source of potassium, a source of sulfur, and additional macronutrients and/or micronutrients, and that do not require the use of chelated metals or chelated metal salts, and that will not form insoluble precipitates.